L8124 Aquastat Settings

Mike F

If you want hi eff you do not want a tankless. you want an indirect. tankless is like sitting at a traffic light all day with your foot on the gas.

Rodney Summers

Most Efficient L8124 Settings?

I have a Weil-Mclain WTGO-4 hot water boiler (base board hot water heat) with a tankless coil set up for domestic hot water. With that, I have a Honeywell 8124 Aquastat with a HI, LO and Diff setting. Obviously, with the price of oil, I don’t want to use one more drop than I have to, to provide for DHW and to heat the house.

I have been reading a lot of various opinions on where and how to set the aquastat settings. With that, I have set mine as follows:

HI-190
LO-140
DIFF-25

Will these settings result in efficient use of the boiler? Any suggestions?

(Weil Mclain says I should set them for HI- 210 LO-190 DIFF-25. For DHW, isn’t 190 ridiculously high)?

Joe Brix

On an 8124

The low limit will kick on at low-limit - 10° (so @ 130° in your setting). You'll be pulling water through your tankless coil at this temp so if you realy draw alot of hot water quickly you'll run cold. When the boiler fires, it will bring the boiler up to Low+ differential. (so 165° in your settings). If your thermostats call for heat, the boiler will go to high limit value unless the thermostat is satisfied first. At high limit the boiler will shut-off and come on again at high limit - 10° (180 in your settings) if there's still a demand from the thermostat.

Rodney Summers

L8124 Settings

Joe: That explains the way it works perfectly, but am I getting the most efficiency out of the boiler? I'm figuring that for space heating, even if the thermostat calls for heat, and the water temp happens to be at 140 and the burner fires, why not start to run the water throgh the baseboard at that temp, rather than wait till the water reaches the 190 setting suggested by Weil-Mclain? With that, I'm thinking why leave all that heat in the boiler before it starts to circulate.

Ron Schroeder

The circ will start wherever it is between 130 and 155 if the low limit isn't calling for heat or at 155 if it was calling for heat.

You can lower the high limit to as low as 160 (if you have enough radiation) and get more efficiency.

Ron

Rodney Summers

L8124 Aquastat settings

Hello Ron.

So are you saying that if there is no call for DHW heat, but there is a call for space heat, that the circ will start between 130 & 155, but if there was a call for DHW heat, then the circ would not start till 155?

Also, did not realize I can go as low as 160 for space heat. I'll try it to see if the house will carry it, especially in the colder months.

Thanks

Joe

Joe Brix

with a tankless coil

there is no "call" for heat. the water flowing through will cool the boiler down to the low limit triggering the burner.

On my L8124L, the circ will always run as long as the "TT" (thermostats contacts) are closed, regardless of the temp of the boiler. Differential only apllies to the what the low limit will fire up to.

Ron Schroeder

Hi Joe,

That's correct.

Basicly the Low Limit part of the aquastat controls both the the burner (when there is no call for heat on the TT terminals) and the circ. When the Low Limit contacts are closed and running the burner (to keep a minimum temperature for the tankless), the other contact is open preventing the circ. from running. So if you raise the Low Limit setting, you also raise the temperature that the aquastat will allow the circ. to run.

If the burner was already running to satisfy the Low Limit when there is a call for heat from the TT terminals, the boiler would have to get up to 155 degrees before the circ. would start.

If the burner was not running when there is a call for heat from the TT terminals, then the circ. would start immediatly.

Ron

Anthony Menafro

Indirect

Amen to that brother!
Anthony

Tony G

Indirect

Then let's take it one step further. If you install an indirect, then what would you set the aquastat too? Using the same boiler and honeywell mentioned.

Ron Schroeder

On my own system, I have the low limit set at about 125-130 with the differential set for 25 and the high limit at 190 but I also have a reset control that keeps the boiler much lower than the high limit except when the indirect calls for heat.

When it is not the heating season, I change the low limit to cold start. I have a high differential on the indirect aquastat so the burner only comes on 5 or 6 times a week in the summer. It doesn't make sense to keep my boiler warm 24/7 except in the heating season. The boiler is a Buderus G115-21, the smallest one.

Ron

Tony G

Unfortunately, I have a Weil Mclane and cna't make it a cold start. Next summer I will be adding a indirect and was looking for some guidance as to the hi and lo limit setting.